Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.62   5.816%   $63.0875   $63.09   $63.10   $63.10  
  Purchase #2 $228.82   10.312%   $252.4159   $252.42   $252.40   $252.40  
  Purchase #3 $43.32   11.308%   $48.2186   $48.22   $48.20   $48.20  
  Purchase #4 $64.39   12.284%   $72.2997   $72.30   $72.30   $72.30  
  Purchase #5 $245.61   8.732%   $267.0567   $267.06   $267.05   $267.10  
  Purchase #6 $62.56   12.305%   $70.258   $70.26   $70.25   $70.30  
  Purchase #7 $250.61   10.416%   $276.7135   $276.71   $276.70   $276.70  
  7 purchase totals = $954.93       $1,050.0499   $1,050.06   $1,050.00   $1,050.10